This content originally appeared on DEV Community and was authored by Parth Agarwal
A different implementation of constant for python
I couldn't find a good implementation of constants, so created my own! Let's get started!
Do checkout the complete code at https://gist.github.com/ra101/aa27ff6e437f74ca56027a8c6b166882
How it Should work
class Links(ConstantClass):
GITHUB = "https://github.com/ra101"
WEB = "https://ra101.github.io/"
LINKS = "dev.ra.101@protonmail.com"
class Author(ConstantClass):
NAME = "〈 RA 〉"
WEB = Links.WEB
LINKS = Links
Now Links.GITHUB should return https://github.com/ra101 and
Link.GITHUB = 'new_value' or Links.NEW_CONTANTS = NEW_VALUE both should return None, without assigning or creating new field
Here is How I made it!
1) We need to mock all setter in a meta class, which will be used by main class.
class ConstantMeta(type):
"""
Meta Class for Constant, How Constant class would behave
"""
def __setattribute__(self, *args, **kwargs):
# Override set method to make it immutable
pass
def __setattr__(self, *args, **kwargs):
# Override set method to make it immutable
pass
def __setitem__(self, *args, **kwargs):
# Override set method to make it immutable
pass
def __set__(self, *args, **kwargs):
# Override set method to make it immutable
pass
1.5) Lets add a external setter
def __force_set__(self, name, value):
# A external set method to make sure we can update value in __new__
return super().__setattr__(name, value)
2) Override __new__ to make the actual class
def __new__(cls, clsname, bases, clsdict):
"""
adding __keys__, __values__ fields
and keys(), values() methods
"""
obj = super().__new__(cls, clsname, bases, clsdict)
obj.__force_set__("__values__", [])
obj.__force_set__("__keys__", [])
for key, val in vars(obj).items():
if not key.startswith("__"):
obj.__values__.append(val)
obj.__keys__.append(key)
obj.__force_set__("keys", lambda: obj.__keys__)
obj.__force_set__("values", lambda: obj.__values__)
return obj
2.5) Add below methods for polishing the class
def __getitem__(cls, key):
# adding __getitem__ to make objects "subscriptable"
return getattr(cls, key)
def __iter__(cls):
# In case of for loops
return zip(cls.__keys__, cls.__values__)
3) Finally Lets create the class!
class ConstantClass(metaclass=ConstantMeta):
"""
Now this class can be inherited whenever required to make constants
"""
pass
Finally! We are Done! We Created a almost immutable class that could be used as constants
Examples
Input:
class Links(ConstantClass):
GITHUB = "https://github.com/ra101"
WEB = "https://ra101.github.io/"
LINKS = "dev.ra.101@protonmail.com"
class Author(ConstantClass):
NAME = "〈 RA 〉"
WEB = Links.WEB
LINKS = Links
Links.WEB = 'any_new_value'
print(f"\nLinks.WEB: {Links.WEB}")
print(f"\nAuthor.values(): {Author.values()}")
print(f"\ndict(Author): {dict(Author)}")
print("\nfor key in Author.LINKS.keys()")
for key in Author.LINKS.keys():
print(f'getattr(Author.LINKS, "{key}"): {getattr(Author.LINKS, key)}')
Output:
Links.WEB: https://ra101.github.io/
Author.values(): ['〈 RA 〉', 'https://ra101.github.io/', <__main__.ConstantClass object at 0x00000293A94768E0>]
dict(Author): {'NAME': '〈 RA 〉', 'WEB': 'https://ra101.github.io/', 'LINKS': <__main__.ConstantClass object at 0x00000293A94768E0>}
for key in Author.LINKS.keys()
getattr(Author.LINKS, "GITHUB"): https://github.com/ra101
getattr(Author.LINKS, "WEB"): https://ra101.github.io/
getattr(Author.LINKS, "EMAIL"): dev.ra.101@protonmail.com
Do checkout the complete code at https://gist.github.com/ra101/aa27ff6e437f74ca56027a8c6b166882
This content originally appeared on DEV Community and was authored by Parth Agarwal
Parth Agarwal | Sciencx (2021-10-02T18:58:26+00:00) Python: Reimaging Constants. Retrieved from https://www.scien.cx/2021/10/02/python-reimaging-constants/
Please log in to upload a file.
There are no updates yet.
Click the Upload button above to add an update.